This invention relates in general to fiber optic ring gyroscopes and more particularly to a passive resonance ring gyroscope configured to have high common mode noise rejection.
The use of fiber optic rings in either interferometer systems or passive resonance systems for the measurement of angular rotation rates is now a well developed technology. Both types of system depend upon measuring the Sagnac shift produced by rotation of the ring, and employ laser beams coupled to the ring such that they travel around the ring in opposite directions to establish the basic interference or resonance pattern. Different variations of such systems are discussed in the following references.
______________________________________ U.S. Pat. No. Issue Date ______________________________________ U.S. Pat. No. 4,274,742 June 23, 1981 U.S. Pat. No. 4,491,413 January 1, 1985 U.S. Pat. No. 4,661,964 April 28, 1987 U.S. Pat. No. 4,673,293 June 16, 1987 U.S. Pat. No. 4,702,600 October 27, 1987 ______________________________________
"Fiber Optic Laser Gyro Signal Detection and Processing Technique" by Martin and Winkler, SPIE Vol. 139, Guided Wave Optic Systems and Devices (1978), pp. 98-102;
"Techniques For Shot-Noise-Limited Inertial Rotation Measurement Using A Multiturn Fiber Sagnac Interferometer" by Davis and Ezekiel, SPIE Vol. 157 Laser Inertial Rotation Sensors (1978) pp. 131-136;
"Technology Assessment of Passive Optical Gyros, Part I, Overview of Concepts, Problems, and Approaches" by Coccoli, September, 1982;
"Passive Ring Resonator Method for Sensitive Inertial Rotation Measurements in Geophysics and Relativity" Saunders, Prentiss and Ezekiel, Optics Letters, Vol. 6, No. 11, pp. 569-571;
In general in a resonant fiber optic ring gyroscope a laser light source is coupled to the fiber optic ring through waveguides which provide for introducing counter propagating light beams into the fiber optic ring. Photodetectors are positioned to measure a portion of the light emanating from the ring. According to the Sagnac effect, rotation of the ring changes the effective path length for light, thereby changing the resonant frequency. If feedback is employed to maintain the frequency at a specific value, then the amplitude of the light waves emitted will vary.
A variety of configurations of passive and active fiber optic gyroscopes have been employed together with accompanying circuitry with the overall objective of increasing the signal to noise ratio. The sources of noise include fluctuations in the path length due to mechanical stresses and thermal changes, as well as noise in the electronics.